Since you're new here, I'm going to just straight out say it: Seattle can be an unwelcoming city to see live music in if you're not 21. It's due to the weirdo liquor licensing laws (minors cannot be where alcohol is sold because we will obviously lose our shit if we are within feet of it). It happens to everyone: The tour announcement comes for one of your favorite bands, your heart starts racing, you click on the event page and see a little "21+" at the bottom, and you want to cry or scream or kick something. But! Don't lose hope. The Stranger prints a small "A" next to all-ages shows in our printed calendar. In our online calendar—strangerthingstodo.com—there's an "all-ages" option on the music calendar. And many of the following venues are always (or mostly) all ages.
The Vera Project
Vera's slogan is literally "Always All Ages," so you won't have a problem here. Vera brings in up-and-coming artists and also books a lot of local acts. The venue is cool and the artists always put on a great show, so you'll definitely want to check something out here.
The Croc is one of my favorite venues, due to the size and the bands that they bring through. They have a little area for the under 21 people to be contained in, which is a fraction of the size of the 21+ area, even though the majority of the crowd is often under 21. I call this the kiddie corral, and its existence really makes me hate the state liquor board, but it's worth sticking it out in the kiddie corral to see a band you love.
Paramount, Moore, Neptune
These venues, managed by STG, are some of the largest in town, so they are constantly bringing in the biggest artists. All three venues are beautiful, quirky and nearly always all ages.
Showbox and Showbox Sodo
Both Showbox and Showbox Sodo bring through larger acts. The Showbox is my favorite of the two, with a smaller room and, in my opinion, cooler bands.
Neumos can be tricky, as they're booking more and more 21+ shows as of late. However, it does also have all-ages shows, its location cannot be beat, and they book some pretty stellar bills. Be sure to check the event for details before you buy.
The Black Lodge
Nestled away in a secret location, this DIY venue throws lots of fun shows with local bands, as well as bands coming through from out of town. Make some friends, ask around, and definitely check this place out if you get the chance. It's one of my favorites.
Office Space is another DIY venue whose location is not publicized, but the bands they book are worth the trouble of finding the spot.
One of the newer DIY venues, they're increasing the frequency of shows lately.
Abbey Arts, which includes Fremont Abbey and Ballard Homestead, have collectively been putting on all ages shows for over 12 years. Abbey Arts hosts all sorts of events in addition to converts too, like art shows, spoken word, and even dance classes.
From time to time, record shops will host free sets with bands, and they're definitely worth checking out. I've seen Cage the Elephant at Easy Street Records in West Seattle, and Sylvan Esso at Sonic Boom Records in Ballard. Go to those stores, ask about upcoming events, and keep your eyes peeled for show posters—or just read The Stranger's music calendar.
If you're into electronic music, more than likely you'll be heading into Sodo for an off the grid warehouse gig. Luckily since these events are already illegal, they also don't care how old you are!
Your Friend's House
Some of my favorite Seattle shows have been DIY house shows. Make musical friends, and in no time you'll be heading to someone's living room for a set.
Other venues that sometimes host all-ages shows: El Corazon, Funhouse, Chop Suey, Studio Seven, Jazz Alley, and Royal Room. Again, check The Stranger's calendar for all the info.